The present invention relates to an optical recording and reproducing system.
FIG. 5a shows a conventional optical reproducing system having a block plate as a beam profile conversion plate. A laser beam 1a emitted from a laser 1 is paralleled at a collimator lens 2 and converged at a condenser lens 3. A block plate 4 is provided between the lenses 2 and 3 on an optical axis of the beam.
The laser beam 1a has luminous intensity as shown by a dotted line of FIG. 5b. When the laser beam 1a is blocked by the block plate, the luminous intensity thereof becomes as shown by a solid line of FIG. 5b at a point A. After the beam passes through the condenser lens 3, the luminous intensity becomes as shown by a solid line of FIG. 5c at a point B. Thus, a spot for a super-resolution is obtained.
FIG. 6a shows another conventional optical system. A beam profile conversion filter plate 6 having a pinhole 7 is provided after a condenser lens 5 for eliminating side lobes 1b appearing in the super-resolution spot of FIG. 5c. The laser beam has luminous intensity as shown in FIG. 6b. When the beam passes the pinhole 7 of the filter plate 6, side lobes are eliminated.
However, in these systems, it is necessary to dispose each of the plates 4 and 6 in the respective optical systems with positioning accuracy. In the former system, it is necessary to dispose the block plate 4 on the line of the optical axis of the beam. Otherwise, a desired super-resolution spot can not be obtained.
In the latter system, it is necessary to coincide the pinhole 7 of the filter plate 6 with a converging position of the condenser lens 5. Otherwise, elimination of side lobes becomes incomplete.